JPS5814251B2 - Chitsuso San Kabutsuno Setsushiyokukangenhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for catalytic reduction of nitrogen oxides, and in particular, to a method for catalytic reduction of nitrogen oxides, in which a gas containing nitrogen oxides, sulfur oxides, and oxygen is transferred to cation-exchanged faujasite-type zeolite. In the presence of a catalyst comprising a base metal component supported,
The present invention relates to a method for removing nitrogen oxides from flue gases by contacting them with ammonia.

Methods for removing nitrogen oxides in flue gas by catalytic reduction include (1) a non-selective reduction method using carbon monoxide, hydrogen or lower hydrocarbons as a reducing agent; and (2)
There are two typical selective reduction methods that use ammonia as a reducing agent. Due to its high rate, it has attracted attention and various methods have been proposed.

In other words, the conventionally proposed catalytic reduction method of nitrogen oxides using ammonia as a reducing agent is a method using a catalyst containing a noble metal such as platinum or palladium as an active component, and a method using a catalyst containing a noble metal such as platinum or palladium as an active component.
It is broadly divided into methods that use a catalyst containing a compound of a base metal such as iron, vanadium, chromium, molybdenum, or iron as an active ingredient.

The active components of these catalysts are mainly supported on alumina, but noble metal catalysts have the disadvantage that they are significantly poisoned by sulfur oxides contained in exhaust gas.

On the other hand, base metal catalysts are relatively less susceptible to poisoning by sulfur oxides, but their activity in the reduction reaction of nitrogen oxides is insufficient, and it is necessary to raise the reaction temperature and lower the space velocity. Become.

However, the amount of exhaust gas to be treated is large;
In addition, since the exhaust gas temperature is generally low, there is a strong desire to develop a highly active catalyst that can be used even under reaction conditions of lower temperature and high space velocity.

Against this background, the present inventors conducted various studies aimed at developing a method that can effectively remove nitrogen oxides under slow reaction conditions of low temperature and high space velocity. In the presence of ammonia, the gas contained in the zeolite is brought into contact with a catalyst formed by impregnating and supporting a base metal component on a zeolite in which the alkali metal is limited to a specific amount by cation exchange. It was discovered that nitrogen oxides can be efficiently reduced and removed, and the present invention was completed.

That is, in the present invention, ammonia is added to a gas containing harmful nitrogen oxides, and this gas mixture is treated with a faujasite-type zeolite to dealkalize the alkali metal to 0.2 to 0 per duram atom of aluminum. A hydrogen-type zeolite containing in the range of 6 equivalents is prepared, and this hydrogen-type zeolite is used as a carrier, and it is brought into contact with a catalyst formed by impregnating and supporting one or more base metal components under conditions that do not cause ion exchange. The present invention relates to a method for catalytic reduction of nitrogen oxides, which is characterized by the following.

The first feature of the catalyst used in the practice of the present invention is that a faujasite-type zeolite, which has been adjusted by cation exchange to contain a specific amount of alkali metal, is used as a catalyst carrier.

That is, the alkali metal in the faujasite type zeolite is 0 per aluminum duram atom in the zeolite.
．． The amount is adjusted to be in the range of 2 to 0.6 equivalents.

The aluminum in the zeolite mentioned here is the aluminum present in the crystalline aluminosilicate that has been neutralized by binding with an alkali metal, and is added as a binder or diluent when molded as a catalyst or carrier. It does not contain aluminum contained in substances such as alumina sol, alumina, and silica alumina, or aluminum cations introduced by exchanging with alkali metals or alkaline earth metals through ion exchange.

The second feature of this catalyst is that the base metal component having a nitrogen oxide reducing action is supported on the carrier by impregnation rather than by ion exchange.

The faujasite-type zeolite used in the catalyst of the present invention is a known one consisting of crystalline aluminosilicate, and generally has a methane-type structure in which Si04 tetrahedrons and AI04 tetrahedra share one set of oxygen atoms with each other. chain-like,
It has a skeleton with a layered or three-dimensional network structure.

Since the AI04 tetrahedron has one negative charge, the corresponding cation binds thereto, and the crystal water is held by the electrostatic attraction of the cation.

Cations are generally alkali metal ions such as sodium and potassium.

The space surrounded by the network structure of the Si04 tetrahedron and the AI04 tetrahedron forms a pore path in which cavities are connected.

Crystal water is present in this, but by heating it, it is desorbed and becomes a porous adsorbent.

The substance to be adsorbed is adsorbed into the cavities or channels through the pores of the aluminosilicate network.

The pores have a uniform diameter, resulting in a molecular sieve effect.

That is, by adsorbing only molecules with a molecular diameter smaller than the pore diameter, they are separated from molecules with a larger molecular diameter.

Zeolites are classified according to pore diameter and SiO2/Al2O3 molar ratio, but those having pore diameters in the range of about 3-15 Å and Si02/Al2O3 molar ratios in the range of about 2-6 are suitable.

Faujasite-type zeolites suitable for the purpose of the present invention include synthetic faujasite and natural faujasite (
Houjas stone) etc. can be used.

Synthetic faujasite contains A-type zeolite 1.0±0.2M2/nO:Al20
3:1.85±0.5 SiO2:YH2 (where M is a metal, n is the valence of M, and Y is a value of about 6 or less.

)X type zeolite 1.0±0.2M2/nO:Al2
03:2.5±0.5SiO2:YH20 (wherein M is a metal with a valence of 3 or less, n is a valence of M, and Y is a value of about 8 or less.

) Y-type zeolite 0.9±〇. 2Na20: Al
203:WSiO2:YH20 (where W is a value of 3 to 6, and Y is a value of about 9 or less.

) etc. are included.

Particularly preferred zeolites are those with pore diameters in the range of about 6-13 Å and a SiO2/Al2Oa molar ratio of about 2 or greater.

For example, a pore diameter of about 8-9 Å and a SiO of about 2-3
Type X zeolite, a type of synthetic faujasite with a molar ratio of 2/Al203 or type Y of another synthetic faujasite with a pore diameter of about 8-9 Å and a molar ratio Si02/A12O3 of about 4-6 or more Zeolites are preferred.

The faujasite type zeolite used as a support for the catalyst according to the present invention has 0.2 to 0 per duram atom of aluminum.
．． 6 equivalents, preferably 0.2 to 0.4 equivalents of alkali metal.

To reduce the content of alkali metals, raw zeolites containing alkali metals can be mixed with solutions containing ammonium cations, such as ammonium chloride, ammonium sulfate, ammonium bromide, ammonium carbonate, ammonium carbonate, ammonium bicarbonate, bromide. ammonium,
Once or twice at room temperature or heating with solutions of inorganic and organic ammonium compounds such as ammonium sulfide, ammonium nitrate, ammonium formate, ammonium acetate, ammonium hydroxide or tetraalkylmethylammonium (tetramethylammonium etc.), tetramethylammonium hydroxide. This can be achieved by making contact more than once.

As mentioned above, the first feature of the catalyst of the present invention is that the alkali metal content is limited, and when the residual amount is 0.6 equivalent or more per duram atom of aluminum in the zeolite, If the amount is 0.2 equivalent or less, high selectivity cannot be ensured in the reduction reaction of nitrogen oxides, as shown in the comparative example below.

In addition to the above-mentioned cation exchange with ammonium ions, methods for reducing the alkali metal content include zeolite in a solution containing hydrogen ions, such as mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, and carbonic acid, or formic acid, acetic acid, propionic acid, etc. Alkali metal ions can be exchanged with hydrogen ions by direct contact with organic acids, or cation exchange with rare earth element ions, such as cerium, lanthanum, etc., can also be employed.

The most preferred method for the catalysts of the present invention is to reduce the resulting ammonium ion-containing zeolite to about 350-700% after treatment with a solution containing ammonium ions.
This is a method in which ammonia is removed and converted into hydrogen ions by firing at a temperature in the range of °C.

In ion exchange, water or an organic solvent can be used as a medium for a solution containing ammonium ions and hydrogen ions.

Water is the most preferred medium from an operational or equipment standpoint.

Organic solvents can also be used as long as they can ionize the compounds used, such as ammonium compounds.

For example, solvents such as alcohols such as methanol, ethanol, gropanol, butanol, amides such as dimethylformamide, diacetoacide, etc., ethers and ketones are suitable.

Examples of embodiments of the method of ion exchange with ammonium ions are as follows.

That is, the alkali metal content was reduced to a desired range by immersing a synthetic zeolite containing an alkali metal in an aqueous solution of an ammonium compound, or by passing an aqueous solution of an ammonium compound into contact with a packed column of synthetic zeolite. After that, in the presence of oxygen, about 350 to 70
Heating to a temperature in the range of 0°C converts ammonium ions to hydrogen ions.

By the above-described treatment, a hydrogen ion type zeolite containing an alkali metal in an amount of 0.2 to 0.6 equivalent to the aluminum duram atom in the zeolite can be obtained.

The concentration of the ammonium compound aqueous solution, the amount used, the immersion or contact time, the immersion or contact temperature, etc. can be appropriately selected so that a desired amount of alkali metal can be removed.

In order to achieve the object of the present invention, a small proportion of at least one refractory inorganic oxide such as alumina, magnesia, titania, zirconia, hafnia, silica, and diatomaceous earth is added to the zeolite carrier as described above, for example, about 1 to 30% weight%
It can also be blended.

Next, the second feature of the catalyst used in the present invention is that, as mentioned above, the alkali metal is 0% per gram atom of aluminum.
．． Hydrogen ion type zeolite containing 2 to 0.6 equivalents,
The purpose is to support base metal components by impregnation.

The hydrogen ion type zeolite that partially retains the alkali metal ions has a large amount of acidic points and has the ability to adsorb a large amount of ammonia on its surface.

Moreover, it does not easily cause ion exchange with base metal ions.

As the base metal component, one or more selected from the group of copper, iron, vanadium, molybdenum, chromium, tungsten, etc. is used.

The most preferred metal component is one or more selected from the group of copper, iron and vanadium.

Suitable forms of the base metal component include metals, metal oxides, metal sulfates, or mixtures thereof.

In particular, preferred forms are sulfates for copper and iron and oxides for chromium and vanadium.

The base metal component in the catalyst is in a catalytically effective amount, e.g. in the range of about 1 to 20%, preferably about 2 to 10% by weight as metal, and the concentration of the metal compound in the impregnating solution, soaking temperature and soaking time, etc. It can be adjusted by

Impregnation of the base metal component into the zeolite is carried out by immersing the zeolite in a solution in which a soluble metal compound is dissolved in a suitable solvent.

As the soluble metal compound, a decomposable compound that is converted into an oxide by firing is used.

Preferred metal compounds are inorganic salts such as nitrates, chlorides and sulfates, and organic salts such as acetates, tartrates and oxalates.

Impregnating solutions of base metal components are made by combining these compounds with water, mineral acids,
It is prepared by dissolving it in an organic solvent or a mixed solvent thereof.

As the mineral acid, nitric acid, hydrochloric acid, sulfuric acid, etc. can be used after diluting with water.

Suitable organic solvents include alcohols, aldehydes, amines and esters.

Examples of alcohol include those in the range of C1 to C10, especially isopropyl alcohol, n-butyl alcohol,
It is preferable to use isobutyl alcohol, pentanol, isopentanol, etc., and as the aldehyde, those in the range of C1 to CIO, particularly acetaldehyde, ethylaldehyde, probilaldehyde, etc., are used.

Further, as the amine, an alkyl amine such as dimethylamine or triethylamine can be used, and as the ester, an organic acid alkyl ester such as ethyl formate, ethyl acetate, isoprobyl acetate, or butyl acetate can be used.

As a base metal component, for impregnation with copper component, copper nitrate,
By immersing the zeolite produced as described above in an aqueous solution of copper chloride or copper sulfate, it can be impregnated with a copper component.

Impregnation is carried out under conditions where ion exchange does not occur.

A particularly preferred immersion temperature is room temperature, and the immersion time is about 5
Select as appropriate within the range of 1 minute to 1 hour.

This is an extremely short time compared to the ion exchange method.

After impregnation with the base metal component, the catalyst is separated from the solution, dried and calcined.

Drying is carried out in the presence or absence of oxygen from about 80 to
This is done by heating to a range of 150°C.

In addition, firing is performed at approximately 300 to 700 ml in the presence of oxygen.
This is done by heating to a temperature range of .

As a result of such treatment, the base metal components typically have an oxide form.

The shape of the catalyst is not particularly limited, and any shape may be used as long as it has a large number of contact surfaces and facilitates gas flow, such as a cylindrical shape, a spherical shape, or a Raschig ring shape.

According to the invention, nitrogen oxides can be prepared by adding ammonia to a gas containing nitrogen oxides and oxygen and contacting the resulting gas mixture with the aforementioned catalyst to selectively reduce the nitrogen oxides. It is to be removed from

In particular, the present invention is suitable as a method for selectively removing nitrogen oxides by treating a gas containing nitrogen oxides, sulfur compounds, and oxygen.

Reduction of nitrogen oxides involves converting them into nitrogen as shown in the following formula, thereby rendering the nitrogen oxides harmless.

6NO+4NH3→5N2+6H20 3NO2,000 4NH3→7/2N2+6H20 Nitrogen oxide-containing gases that can be treated according to the present invention include flue gas from stationary sources such as power plants and other boilers.

In addition to carbon dioxide, water vapor and nitrogen, such flue gases usually contain nitrogen oxides, sulfur oxides and oxygen.

A typical flue gas composition is as follows:

NOx About 0.01-0.05% SOx About 0.01-0.3% 02 About 3-7% According to the present invention, nitrogen oxides can be efficiently removed in the presence of sulfur oxides and oxygen. I can do it.

The amount of ammonia added to the gas stream is approximately 0.00% of the stoichiometric amount required to reduce nitrogen oxides to completely harmless nitrogen.
7 times or more, that is, when most of the nitrogen oxides are carbon monoxide (.NO), approximately 0% per mole of nitrogen oxides
．． Requires 5 moles or more.

In particular, the preferred amount of ammonia added is nitrogen oxide (N
Ox, x: 1) From about stoichiometric amount to about 1 per mole
．． It is in the range of 5 moles.

In the present invention, even when temporarily adding excess ammonia, the adsorption capacity of the catalyst is large, so ammonia is
No passage into the flue gas effluent.

The gas mixture of nitrogen oxide-containing gas and ammonia is heated to about 200-500°C, preferably about 250-40°C.
Temperature in the range of 0℃, about 2000-10000
0V/H/V, preferably about 5000 to 3
Contact with a fixed bed catalyst under reaction conditions with a gas hourly space velocity in the range of 0 0 0 0 V/H/V.

As described above, the present invention provides a novel method for catalytic reduction of nitrogen oxides in the presence of oxygen, and is a method using a conventionally known alumina-supported catalyst and a base metal ion-exchanged zeolite catalyst. It exhibits extremely superior activity and selectivity even at low temperatures and high space velocities.

Furthermore, while base metal-exchanged zeolite catalysts are poisoned by sulfur oxides and have reduced activity, the zeolite catalysts used in the present invention are less susceptible to the effects of sulfur oxides and can maintain a long life.

Next, Examples and Comparative Examples will be shown to clarify the effects of the present invention, and the drawings in which the results obtained in the Examples and Comparative Examples are graphed will be described.

Figures 1 to 3 show catalyst bed temperature and nitrogen oxides (NOx).
This shows the relationship with removal rate.

According to the method of the present invention, a removal rate of 100% is achieved, and the removal rate is high over a wide range of low temperature and high temperature sides.

In the figure, each curve represents the following items.

Example 1 A copper-supported zeolite catalyst was produced as follows.

In 1000 ml of a 2.1N aqueous solution of ammonium chloride,
Sodium salt 10 of Y-type zeolite, an extruded synthetic faujasite with a diameter of 1.5 mm and a length of 6 mm.
0 g was immersed, and ion exchange was performed at room temperature for about 24 hours with appropriate shaking.

After ion exchange, the zeolite is taken out of the solution, washed with water and dried, and then calcined in air at 500°C for 3 hours to form a catalyst support containing 0.33 equivalents of sodium per duram atom of aluminum in the zeolite. I got it.

50 g of this catalyst carrier was mixed with 100 ml of an aqueous solution containing 3% by weight of copper (Cu) prepared from copper nitrate (Cu(NOs) 23 H2 0 ).
1 and left at room temperature for 30 minutes.

The carrier was taken out from the solution, dried, and then calcined at 500°C for 16 hours to obtain a zeolite catalyst supporting 3% by weight of copper.

20m of copper-supported zeolite catalyst produced as above
A quartz reaction tube with an inner diameter of 18 mm was filled with 50 ppm of A2, 00 ppm of SO2 was added to the fixed catalyst bed.
A gas mixture was introduced in which ammonia was added to a gas with a composition of m, CO2 10%, 023%, ■2010% and the balance N2 so that the concentration was 250 ppm3.
The gas flow rate is 20000V/H/in terms of space velocity.
It was set to V.

The removal rate of nitrogen oxides at each catalyst bed temperature is shown in Curve 1 in Figure 1.

Comparative Example 1 2% by weight of copper (Cu) was added to alumina (
The removal rate of nitrogen oxides was measured for each catalyst bed temperature under the same conditions as in Example 1 using a catalyst supported on γ-alumina (specific surface area: 110 m3/g). The results are shown in curve 2 in Figure 1. .

It can be seen from the figure that the removal rate of nitrogen oxides is low with the copper/alumina catalyst.

Comparative Example 2 A zeolite support containing 0.33 equivalents of sodium per duram atom of aluminum prepared in Example 1 (
B-Y) without supporting copper, with a gas space velocity of 50
When the gas of Example 1 was treated under the conditions of 0 0 V/H/V and a temperature of 200 to 500°C, the nitrogen oxide removal rate was 2.
It was less than 0%.

As described above, the removal rate of nitrogen oxides was low in the case of a zeolite catalyst containing a base metal component and sodium that does not support (copper oxide).

Comparative Example 3 This example shows an example in which a base metal component was supported on a carrier by ion exchange rather than by impregnation.

(A) 1.0 N aqueous solution of copper acetate at 500 mA Example 1
100 g of the same synthetic Y-type zeolite was immersed and ion exchanged at room temperature for about 2 hours with appropriate shaking.

After repeating this operation four times, the zeolite was taken out, washed with water, dried, and calcined in air at 500° C. for 3 hours to obtain a catalyst having 0.42 equivalents of sodium per duram atom of aluminum.

Note that the amount of copper contained in this catalyst was 6.20% by weight.

(B) After carrying out the same ion exchange operation as in A above once, a catalyst containing 0.85 equivalents of sodium per atom of aluminum was obtained in the same manner.

The amount of copper contained in this catalyst is 3.41% by weight.
As for the amount of copper in the catalyst, it can be almost directly compared with the catalyst of Example 1.

When the nitrogen oxide removal rates of these catalysts (A) and (B) were measured for each catalyst bed temperature under the same conditions as in Example 1, the results shown in curves 3 and 4 in FIG. 2, respectively, were obtained.

It can be seen from the figure that the removal rate of nitrogen oxides is low when the ion exchange method is used to carry the base metal components on the carrier.

Example 2 2-(1) Ammonium chloride 0.30N aqueous solution 100
100 g of sodium salt of synthetic Y-type zeolite was immersed in 0 ml of the solution, and an ion exchange operation was performed at room temperature for about 24 hours with appropriate shaking.

After the ion exchange operation, the zeolite is washed with water and dried.
Next, this was calcined in air at 500° C. for 3 hours to obtain a catalyst carrier.

The amount of sodium contained in this was 0.60 equivalent per duram atom of aluminum.

2-(2) Also, ammonium chloride 1.0N aqueous solution 5
100 g of synthetic Y-type zeolite was immersed in 00 ml of the solution, and ion exchange was performed in a water bath at 70° C. for about 4 hours with appropriate shaking, and then the solution was removed by decanting.

This operation was repeated four times. The zeolite carrier was taken out from the solution, washed with water, dried, and then calcined in air at 500°C for 3 hours to obtain a carrier.

The amount of sodium contained therein was 0.23 equivalent per duram atom of aluminum.

Each zeolite carrier obtained by the above method was mixed with copper nitrate [Cu(NO
3) 2.H20] and left at room temperature for 30 minutes.

The copper-supported zeolite was taken out from the solution, dried, and heated to 500
The catalyst was calcined in air at ℃ for 16 hours to obtain a catalyst containing 3.5% by weight of copper.

When the removal rate of nitrogen oxides was measured for each catalyst bed temperature using these zeolite catalysts having different sodium contents under the same conditions as in Example 1, the results shown in curves 5 and 6 in FIG. 3 were obtained.

Comparative Example 4 (A) The same operation as in Example 2-1 was carried out using 0 ammonium chloride.
．． A 1N aqueous solution was used to obtain a zeolite support having 0.65 equivalents of sodium per duram atom of aluminum.

(B) The same operation as in Example 2-2 was repeated a total of 8 times to obtain a carrier containing 0.14 equivalents of sodium per duram atom of aluminum.

The same copper loading operation as in Example 2 was carried out on the two kinds of supports obtained above to obtain a catalyst having 3.5% by weight of copper.

This was evaluated using the same method.

The results are shown in curves 7 and 8 in Figure 3.

The figure shows that when the sodium metal contained in the zeolite is 0.6 equivalent or more per gram atom of aluminum, or 0.6 equivalent or more per gram atom of aluminum.
It can be seen that when the amount is 2 equivalents or less, the removal rate of nitrogen oxides is low.

Example 3 The same procedure as in Example 1 was performed except that the content of sulfur dioxide was changed and the catalyst bed temperature was fixed at 325° C., and the following results were obtained.

Comparative Example 5 The copper-exchanged zeolite catalyst obtained in Comparative Example 3A was evaluated in the same manner as in Example 3.

From the above results, it is clear that high activity can be achieved by setting the alkali metal content in the range of 0.2 to 0.06 equivalents per duram atom of aluminum in the zeolite. Compared to ion-exchange zeolite catalysts, it has excellent activity and selectivity in removing nitrogen oxides at both low and high temperatures, despite the lower content of supported base metal components.

(Example 1 and Comparative Example 3).

Furthermore, it is clear that the activity of the latter catalyst is drastically reduced in the coexistence of sulfur oxides, whereas the former catalyst of the present invention is less susceptible to poisoning and maintains high activity.

Example 4 200 ml of ammonium chloride 0.50N aqueous solution was added with natural faujasite (chemical analysis value in anhydrous state (wt%):
Na20=3.97, CaO=4.87, Mg0
-3.04, A1203=23.3, Sin2=6 4
．． 1) Soak 20g of the powder and shake as needed, about 2
Ion exchange operation was performed at room temperature for 4 hours.

After the ion exchange operation, the zeolite is washed with water and dried.
Next, this was calcined in air at 500° C. for 3 hours to obtain a catalyst carrier.

This carrier (chemical analysis value (wt%): Na20 = 2.98
, CaO = 2.83, MgO = 1.8 2AI2O
3=24.5, Si02=67.2), the amount of sodium contained was 0.20 equivalent per duram atom of aluminum.

The zeolite carrier obtained by the above method has a diameter of 3 mm and a height of 3 to 3 mm.
After compression molding to a size of 4 mm, a catalyst carrying 3.5% by weight of copper was obtained in the same manner as described in Example 2.

The removal rate of nitrogen oxides was measured for each catalyst bed temperature using this catalyst under the same conditions as in Example 1, and the following results were obtained.

Examples 6-7 and Comparative Examples 6-7 Except for using the sodium salt of Y-type zeolite, which is a synthetic faujasite, and changing the ammonium chloride concentration, operation time, temperature, and number of operations during ion exchange operation. The same operation as in Example 2 was carried out to obtain copper-supported zeolite catalysts having different sodium contents.

The nitrogen oxide removal rate of each of the zeolite catalysts thus obtained was measured under the same conditions as in Example 1 at each catalyst bed temperature.

The results are shown below along with the conditions for the ion exchange operation.

Next, embodiments of the present invention will be summarized.

■ By adding ammonia to the flue gas containing harmful nitrogen oxides and converting this gas mixture into (2) Calcining the synthetic faujasite obtained by the above treatment; (3) Using the hydrogen-type synthetic faujasite obtained by the calcination as a phase, one or two A method for the catalytic reduction of nitrogen oxides, which comprises contacting at least one base metal component with an impregnated and supported catalyst under conditions that do not cause ion exchange.

■ By adding ammonia to the flue gas containing harmful nitrogen oxides and treating this gas mixture with (1) a synthetic faujasite with an aqueous solution containing hydrogen ions, the alkali metal is reduced to 0.2 per duram atom of aluminum. (2) Using the hydrogen-type synthetic faujasite obtained by the above treatment as a phase, one or more base metal components are impregnated and supported under conditions where ion exchange does not occur. A method for catalytic reduction of nitrogen oxides, characterized by bringing the nitrogen oxides into contact with a catalyst comprising:

[Brief explanation of drawings]

FIG. 1, FIG. 2, and FIG. 3 are graphs showing the effects of the present invention.

Claims (1)

[Claims] 1. When ammonia is added to a gas containing harmful nitrogen oxides and the gas mixture is brought into contact with a catalyst to reduce and remove the nitrogen oxides, a faujasite-type zeolite is used as a catalyst to dealkalize the alkali metal. A hydrogen-type zeolite containing 0.2 to 0.6 equivalents per duram atom of aluminum is used, and one or more base metal components are added to this hydrogen-type zeolite as a carrier under conditions that do not cause ion exchange. A method for the catalytic reduction of nitrogen oxides, characterized in that a catalyst is impregnated and supported on the catalyst.